Stereological studies on the gametogenic cycle of the scallop, Pecten maximus, in suspended culture in Ria de Arousa (Galicia, NW Spain)

Abstract

Samples of Pecten maximus cultured using the ear-hanging technique were collected at regular intervals from April 1990 to July 1991. The gametogenic cycle has been studied in relation to the environmental conditions (temperature, chlorophyll a and seston) and assessed by two different methods: determination of the gonad condition index and study of the oocyte diameter by image analysis following a Stereological technique. Two principal spawning periods were found, the first one in late spring and early summer (May–June 1990, June–July 1991), the second one in winter (February–March 1991). The temperature ranges from 11 to 21 °C with maxima in July and minima in December. Low temperatures during maturation gave rise to a delay in the spawning period. Spring spawning appears to occur after a threshold temperature around 16 °C is reached, whereas winter spawning takes place at lower temperatures (12–13 °C) and can be triggered by a phytoplankton bloom. Minor spawnings may be possible in late summer and at the beginning of autumn. No sexual resting period exists. The number of atretic oocytes were very high throughout the year. Oocyte lysis appears to be a common process linked to the reproductive strategy.